1. Field of the Invention
The present invention relates to a method for preparing three types of benzidine compounds in a specific ratio, and more particularly to a method that prepares three desired types of benzidine compounds in specific chemical structures and in a desired ratio by using only one synthesizing step.
2. Description of Related Art
Benzidine compounds are important materials for photochemistry because of their electrical characteristics and are widely used in organic electroluminescence devices, light emitting diodes, xerographics, and charge transporting layers in printing machines.
A conventional method for preparing the benzidine compounds for a charge transporting layer is by using a metal catalyst such as copper, nickel, or palladium in cooperation with various ligands to couple halogenated benzene and diphenylamine into the benzidine compounds at high temperature. In order to make the charge transporting layer have excellent electrical characteristics, several desired kinds of benzidine compounds have to be mixed in a specific ratio to compose a composite material for the charge transporting layer. However, in the conventional method each kind of benzidine compound is prepared individually and then mixed with each other so that the conventional method is troublesome and time-wasting and has high manufacturing cost. Additionally, mixing the different kinds of benzidine compounds to compose a mixture of the benzidine compounds is hard to precisely control so that all batches are consistent, and so each batch of the mixture has differences in the quantity of added individual benzidine compounds. Therefore, the quality and the electrical characteristics of the mixture in different batches are irregular.
The present invention has arisen to provide a method for preparing three types of benzidine compounds in one step to overcome and obviate the drawbacks of the conventional method.